Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders among reproductive-age women, affecting ~5-10 percent of women in the general population. Clinical features of PCOS include chronic anovulation, androgen excess, and polycystic ovaries, with insulin resistance considered a central factor. In women with PCOS who do get pregnant, limited data suggest there may be a higher incidence of pregnancy complications, including gestational diabetes and hypertensive disorders. However, these investigations have been conducted in only selected groups and there have been no large population-based studies of pregnancy outcomes among women with PCOS, and extremely limited data on relevant neonatal outcomes. The membership of Kaiser Permanente Northern California, one of the largest integrated health care delivery systems in the US, presents a unique opportunity to investigate the epidemiology and pregnancy-related outcomes of women with diagnosed PCOS within a large multiethnic population. Using the Kaiser Permanente PCOS Registry, which includes -13,000 women with diagnosed PCOS, in addition to automated electronic data sources and targeted chart review, we propose to evaluate whether specific gestational and neonatal adverse outcomes are associated with PCOS, and potential mediating factors. The three Specific Aims of our study are the following: AIM 1. To evaluate the effects of PCOS status on the incidence of gestational diabetes, gestational hypertension, and pre-ecclampsia/ecclampsia among pregnant women. AIM 2. Among the subset of women with PCOS who become pregnant, to identify clinical, metabolic and reproductive factors which predict an increased risk of gestational diabetes and pre-ecclampsia/ecclampsia. AIM 3. To evaluate the association of maternal PCOS status with the incidence of adverse neonatal outcomes, including macrosomia, premature delivery and neonatal intensive care unit (NICU) admission. Secondarily, we will evaluate the association of PCOS status with the incidence of small-for-gestational-age infants and overall neonatal mortality. The proposed study will provide a rigorous evaluation of the impact of PCOS on pregnancy-related and neonatal outcomes and hopefully yield insights into better risk stratification and development of therapeutic strategies designed to improve perinatal outcomes among the growing population of women with PCOS.